$13.\_\_\_\_$ reflux is a theoretical condition where all the condensed vapor is returned to the column as $\_\_,$ with no $\_\_$ taken off, used to determine the $\_\_\_\_$ number of stages.

$14.$ The $\_\_\_\_$ and $\_\_$ equations are fundamental in designing distillation columns, allowing for the calculation of the $\_\_$ reflux ratio and aiding in understanding the $\_\_\_\_$ between stages and reflux ratio.

$15.$ In multi$-$component distillation, $\_\_\_\_$ feeds and $\_\_$ streams can be utilized to introduce or withdraw $\_\_$ at various points in the column, affecting the $\_\_$ and $\_\_\_\_$ of the separation process.

$16.\_\_\_\_$ distillation is a method used to separate $\_\_$ sensitive to high temperatures, leveraging the fact that $\_\_$ in the presence of water can distill at temperatures below their $\_\_\_\_$ boiling points.